Infiltration of a powder metal skeleton of a similar materials using melting point depressant

ABSTRACT

An infiltrant is used to fill a metal powder skeleton. The infiltrant is similar in composition to the base powder, but contains a melting point depressant. The infiltrant will quickly fill the powder skeleton, then as the melting point depressant diffuses into the base powder, the liquid will undergo solidification and the material will eventually homogenize. This process allows more accurate control of dimensions in large parts with uniform or homogeneous microstructure or bulk properties.

PRIORITY CLAIM

[0001] This claims priority to U.S. Provisional application No.60/206,066, filed on May 22, 2000, the full disclosure of which is fullyincorporated by reference herein.

GOVERNMENT RIGHTS

[0002] The United States Government has certain rights in this inventionpursuant to the Office of Naval Research Award # N0014-99-1-1090,Research in Manufacturing and Affordability, awarded on Sep. 30, 1999.

BACKGROUND

[0003] Traditional manufacturing processes using powder metallurgyinitially produce a near net shape part which is only 50-70% dense.These ‘green’ parts then undergo further processing to achieve fulldensity and the desired mechanical properties. The densification is doneeither by lightly sintering and infiltrating with a lower meltingtemperature alloy or by a high temperature sintering alone. In the firstmethod, the part's dimensional change is typically only ˜1% making itsuitable for fairly large (˜0.5 m on a side) parts, but the resultingmaterial composition will be a heterogeneous mixture of the powdermaterial and the lower melting temperature infiltrant. Sintering thepowder to full density will result in a homogeneous final material, buta part will undergo ˜15% linear shrinkage if it starts out at 60%density. For this reason, full density sintering is typically only usedfor smaller (<5 cm on a side) parts.

[0004] In many critical applications (structural, aerospace, military),a material of homogeneous composition is preferable because ofcertification issues, corrosion issues, machinability, or temperaturelimitations that might be imposed by the lower melting point infiltrant.Further, designers of metal components are not accustomed to workingwith composites of heterogeneous composition, and so this creates apsychological barrier.

GOAL

[0005] The ability to create very large parts with homogeneouscomposition via powder metallurgy builds on all of the benefits of PMprocessing. The key here is in using an infiltration step to densify thegreen part without any significant dimensional change, but resulting ina final material with homogeneous composition. This allows fabricationof homogeneous net shape parts in a wide variety of sizes using solidfreeform fabrication, metal injection molding, or other PM processes.There also exists the potential of matching an existing commercialmaterial system.

SUMMARY

[0006] The general concept is to use an infiltrant to fill a powderskeleton, that is similar to the base powder, but contains a meltingpoint depressant. The infiltrant will quickly fill the powder skeleton,then as the melting point depressant diffuses into the base powder, theliquid will undergo isothermal solidification and the material willeventually homogenize. This process will allow more accurate control ofdimensions in large parts with uniform or homogeneous microstructure.

[0007] To further explain this concept, FIG. 2 shows the phase diagramfor nickel and silicon, an example. At the upper left corner, we seethat the addition of ˜11 wt % silicon can decrease the melting point ofnickel by over 300° C. Choosing an infiltration temperature of 1200° C.,an infiltrant alloy with 10% silicon could infiltrate a pure nickelskeleton. After filling the void space in the skeleton, the siliconwould diffuse into the skeleton until it reached a uniform composition.If the void space in the skeleton was ˜40%, the homogenized materialwould contain ˜4% silicon.

[0008] The success of such an infiltration requires the time scale ofthe infiltration to be much faster than the diffusion of the meltingpoint depressant and the subsequent homogenization. There are varioustechniques that can enhance this tradeoff, but the selection of amaterial system has the greatest impact on the infiltration anddiffusion rate.

DETAILED DISCUSSION

[0009] These and other features, aspects, and advantages of the presentinvention will become better understood with regard to the followingdescription and accompanying drawings, where:

[0010]FIG. 1 schematically depicts a homogenizing infiltration concept;

[0011]FIG. 2 is a Nickel-Silicon equilibrium phase diagram;

[0012]FIG. 3 shows dissolution of a pure nickel skeleton after dippinginto a pool of Ni-11 wt % Si for 5 minutes at 1200° C.;

[0013]FIG. 4 shows schematically use of a phase diagram to calculate howmuch excess nickel to use in presaturating the infiltrant;

[0014]FIG. 5 shows an early part testing overhangs;

[0015]FIG. 6 shows a serpentine skeleton that was dipped in a bath andused to measure infiltration rate;

[0016]FIG. 7 shows a large (˜1 kg) part infiltrated using a gate toprevent premature introduction of the infiltrant to the skeleton;

[0017]FIG. 8 shows a cylindrical skeleton that was infiltrated whilehanging vertically to investigate limits to infiltration height; thisparticular sample filled ˜16 cm;

[0018]FIG. 9 shows schematically that erosion at the base of theskeleton progresses several centimeters into the part;

[0019]FIG. 10 shows a large MIT part that sagged after sintering, whilesuspended;

[0020]FIG. 11 shows a similar part as shown in FIG. 10, where thesagging problem was solved through allowing the part to rest on thecrucible floor and using a different gating mechanism.

[0021] Transient liquid phase (TLP) brazing is commonly used to repaircracks and bond materials together. This traditional process involvesthe mechanism of a melting point depressant diffusing into a basematerial and undergoing isothermal solidification. Narrow gaps arenecessary for the nickel brazing alloys to fill the capillary channeland solidify in a reasonable amount of time. The solidification time islimited by the diffusion of the melting point depressant into the basemetal. Gaps wider than ˜50 μm would result in excessively longsolidification times.

[0022] Wide gap brazing has been developed to allow brazing of gaps inexcess of 100 μm. Powder similar to the base material is used to fillthe gap prior to the addition of the brazing alloy. This allows theliquid brazing alloy to fill large gaps and solidify faster.

[0023] There are two studies from the early 1980's involving theinfiltration of a powder skeleton with the aim of creating a usefulsteel part. Banerjee attempted to use cast iron to infiltrate a skeletonof pure iron. The cast iron would freeze off within a few millimeters ofcontacting the skeleton due to the high diffusivity of carbon. Thorsenwas successful in infiltrating a sintered steel skeleton with a Fe—C—Palloy, but an interconnected network of phosphides resulted in a verybrittle final part.

SPECIFIC EXAMPLES

[0024] Infiltration of a pure nickel powder skeleton with any of thecommercial nickel brazing alloys. The melting point depressants in thepreexisting nickel brazes are phosphorous, boron, and silicon. Thealloys also typically contain other elements that provide additionalstrength such as chromium, iron, molybdenum.

[0025] Infiltration of pure nickel powder skeleton with a binary alloyof nickel and silicon.

[0026] Infiltration of a nickel chromium skeleton with a nickel chromiumsilicon alloy.

[0027] Infiltration of a high melting temperature inconel alloy powderskeleton with a similar alloy containing a melting point depressant suchas boron, phosphorous, silicon, tin or a combination thereof.

[0028] Infiltration of a pure aluminum or aluminum alloy skeleton with asimilar alloy containing silicon or lithium as a melting pointdepressant.

[0029] Infiltration of a pure copper or copper alloy skeleton with acopper silver, copper titanium or other alloy with melting pointdepressed.

[0030] Details of Execution

[0031] Several techniques have been developed and used to overcomedifficulties with diffusion occurring during the infiltration of askeleton.

[0032] Gate Mechanism to Separate Molten Infiltrant from Skeleton

[0033] Physical separation of the liquid infiltrant from the skeletonprevents premature interaction or diffusion before the infiltrationbegins. If the infiltrant is already in physical contact with theskeleton prior to melting, the liquid will begin to wick into the partas soon as it becomes molten. In this case, the melting of theinfiltrant or other transient thermal processes will control theinfiltration rate. Controlling the introduction of the liquid can bedone via a gate that can be actuated at a controlled point in time, oncethe liquid infiltrant has reached the desired steady state temperature.Several such gating mechanisms have been used in practice.

[0034] A simple method is to suspend the skeleton prior to infiltrationand dip it into a bath of the molten infiltrant. If the part is toodelicate to hang under its own weight, then a special mechanism shouldbe used to allow a gated infiltration with the part resting in acrucible. It can be difficult to create a fluid seal that will hold atthe infiltration temperature, but using a crucible material that is notwet by the infiltrant makes a seal possible. Two simple mechanisms havebeen used successfully so far. The first is a vertical alumina plateused to separate the two halves of a rectangular crucible. The shape ofthe plate must match the cross-sectional profile of the crucible, so abisque fired alumina was cut and filed to maintain less than 1 mm gapwhen fitted to the crucible. This gap was sufficient to hold a 2 cm deeppool, but a deeper pool would require closer tolerances or filling ofany gaps with a coarse alumina powder. A more elegant solution is to usean alumina tube with a cleanly cut end to sit vertically with the endflush with the bottom of the crucible. The infiltrant is placed insidethe tube and will contain the melt until the tube is lifted from above.

[0035] Several other methods can be used for gating the infiltration. Acustom crucible could be fabricated with a hole at the bottom. This holecould be plugged with a simple rod to prevent infiltrant flow until therod is removed. Another method is to tip a container of infiltrantallowing the liquid to flow out of the tundish. Further, the vessel usedto contain the infiltrant could be flexible. A woven cloth of aluminafibers has been used to contain liquid metal. A cloth bag could be usedto contain the melt and then opened up to allow the liquid to flow out.

[0036] The actuation of any type of gate requires a linear or rotarymotion actuator passing through the gas-tight shell of the furnace. Inthe case of nickel parts fired in a forming gas atmosphere, thefeedthrough can be a rod sliding through a slightly oversized hole inthe shell. If the internal pressure in the furnace is maintained toseveral inches of water, the leak will not allow air into the furnace tocontaminate the atmosphere. In applications where atmosphere purity ismore critical, several linear and rotary motion feedthroughs areavailable commercially for high vacuum applications.

[0037] Presaturation of the Melt

[0038] If the liquid infiltrant has a composition that is greater thanits equilibrium liquidus composition at a given temperature, it willhave the capacity to absorb additional material from the skeleton anddissolve the part. This can happen very quickly because of the highdiffusivity in liquids. It can be a significant problem especially whena large melt pool is used. FIG. 3 shows a pure nickel skeleton,originally a cylinder, with the bottom section dissolved from when itwas dipped into a pool of molten Ni-11 wt % Si for 5 minutes at 1200° C.Since the equilibrium liquidus composition is less than 10% Si, theliquid absorbs any solid nickel with which it comes into contact.

[0039] If the infiltrant composition is known exactly, the processtemperature could be selected to exactly match the liquidus temperaturefor that composition, but this requires very accurate process control. Amore robust method for ensuring that the liquid is saturated, is to putit in contact with solid and allow it to reach its equilibriumcomposition for whatever process temperature it is at. The liquid mustbe in contact with the solid for a long enough time to reachequilibrium. This time will depend on the surface area of liquid solidinteraction and mass transfer in the liquid, determined by diffusion andconvection.

[0040] For example, to presaturate the nickel silicon infiltrant, excessnickel powder is added to the crucible of infiltrant. The large surfacearea of the powder enables equilibration in a reasonable amount of time.The amount of excess nickel added is important. Too little would resultin it completely dissolving and the liquid still not reaching itsequilibrium liquidus composition. Too much would result insolidification of the infiltrant pool. The appropriate amount isdetermined by considering the extreme cases for a window of processingtemperatures. FIG. 4 illustrates how this would be done for a desiredinfiltration temperature of 1180° C. and maximum temperature variationof 20 degrees. The bulk composition should be chosen from theintersection of the maximum temperature with the liquidus line, markedas A on the figure. This ensures that there will be some solid presentand all the liquid will be saturated with nickel. If the temperature isat the lower limit, this composition will correspond to a ratio ofliquid to solid given by the Lever rule. For this example, at 10% Si and1160° C. it would be approximately 30% solid. This will determine theamount of total infiltrant needed, since only 70% of the infiltrant isguaranteed to be liquid available for filling the part.

[0041] Example Infiltrations

[0042] There are several main considerations that are fundamental tosuccessfully creating homogeneous parts via infiltration of a powderskeleton. Problems arise associated with premature freeze off of theinfiltrant, erosion of the skeleton, and part distortion. This sectionaddresses each of these issues by identifying probable causes andpossible solutions.

[0043] Preventing Premature Freeze-Off of the Infiltrant Before it Fillsthe Skeleton

[0044] As was mentioned earlier, the time for the liquid to fill theskeleton must be significantly shorter than the time it takes fordiffusion of the melting point depressant and the resulting isothermalsolidification. If the alloying element diffuses too quickly, it willfreeze off before the part has filled. Utilizing a gating mechanismduring the infiltration as mentioned under details of execution iscritical to minimizing the infiltration time. The other factors thatcontrol the infiltration rate are based on fluid mechanics.

[0045] The capillary force that draws the liquid into the skeleton iscontrolled by the surface tension of the liquid infiltrant. This forceacts at the solid-liquid interface, which can be controlled by thepowder size. Smaller powder will have a larger driving forceproportional to 1/r. However, the smaller pore size will cause a largerrestriction to the flow due to viscous drag. For flow through acylindrical tube, the viscous drag is proportional to 1/r². This meansthat infiltration should occur faster in a skeleton made from largerpowder.

[0046] There will be a limit to the maximum powder size imposed by thenecessary capillary rise height. If the pore space in the skeleton ismodeled as a cylindrical channel of radius r, the driving force would beequal to 2πr·γ_(st)·cos(θ), where θ is the wetting angle. As the liquidrises, it must supports its own weight, equal to πr²·ρgh. The pore sizeradius must be small enough to yield a capillary rise greater than theheight of a part. Using the value of surface tension for pure nickel at1500° C. (1.7 N/m), assuming perfect wetting, and a part height of 0.5meters, the pore radius must be less than 80 μm.

[0047] We have been able to measure some typical infiltration rates ofthe Ni-10Si infiltrant filling a 50-150 μm nickel skeleton. This wasdone through hanging the skeleton by a wire through the roof of thefurnace and measuring the force increase on the wire. By isolating thesurface tension and buoyancy forces, we were able to relate the force tothe increasing mass of the part due to picking up the liquid. The liquidfilled an 8 cm tall skeleton in approximately one minute. Other liquidmetals have viscosity and surface tension that are similar so this rateshould not change drastically with material system.

[0048] Now we move to discussion of the diffusion rate that will controlthe isothermal solidification of the infiltrant and the eventualhomogenization of the skeleton. Since the liquid fills a small skeletonin approximately one minute, the isothermal solidification would ideallytake place over an hour or two. The diffusion rate will be controlledprimarily by the material system chosen. This was a reason for using Sias a melting point depressant in Ni rather than B or P, which diffusefaster. Diffusivity can have a strong dependence on temperature, sinceit is an activated process that follows an Arhennius dependence.Controlling infiltration temperature allows for some control of thediffusivity for a given material system. Reduced temperature shouldallow more time for the liquid to fill the skeleton before freezing.

[0049] In experimental tests, we have observed much faster masstransport than would correspond to the experimental values ofdiffusivity. It is possible that there is a reaction occurring at thesolid liquid interface. For some material systems, the formation of aparticular phase of intermetallic at the interface could accelerate themass transport. The motion of the solid liquid interface could also beleaving behind solid that is high in composition of the melting pointdepressant.

[0050] Selection of a material system is critical to controlling thetime scale of the isothermal solidification. In particular, thediffusivity of the melting point depressant will have the greatesteffect on the freezing. Using a slower melting point depressant, such astin, could drastically increase the amount of time the skeleton has tofill with infiltrant before freezing begins to occur.

[0051] Coating the powder skeleton (or just the raw powder) with sometype of finite time diffusion barrier would keep the melting pointdepressant from leaving the infiltrant until the liquid has filled thepart. Such a diffusion barrier could be another metal that has a lowerdiffusivity of solute. The thickness of the barrier could be selected sothat it would only last for the duration of the infiltration. It wouldthen allow the solute to diffuse through, allowing isothermalsolidification and eventual homogenization.

[0052] Minimizing Erosion of the Skeleton

[0053] As the liquid infiltrant enters the skeleton, it has a tendencyto leave an erosion path. This occurs to some extent in most powdermetal infiltrations, but it usually is limited to the initial 1 cm atthe base of a part. In those cases, the part to be infiltrated can beplaced on top of a sacrificial stilt where the erosion occurs. In thenickel silicon system, the erosion tends to propagate for severalcentimeters into the part. The appearance is similar to a riverbed andone example is shown in FIG. 9. Studying the erosion pattern on severaldifferent parts suggest, not surprisingly, that the areas of highestliquid flow correspond to where the erosion occurs. Once erosion begins,the larger channel has less viscous drag and would allow more liquid toflow through the newly formed channel. An instability such as this wouldexplain why the erosion progresses so far into the part. Throughmetallographic study of cross sections, the eroded areas are found to behigh in silicon content. This is not surprising since those compositionswould be liquid at the infiltration temperature. The areas of erosionare not limited to the surface, voids have been found within a part in apath of high silicon content.

[0054] Since the infiltrant was presaturated with nickel, it issurprising that more nickel is dissolved (erosion of the skeleton) asthe liquid fills the part. Even if previously saturated, the infiltrantwould have the capacity to absorb additional nickel if it increased intemperature. An exothermic reaction at the solid liquid interface couldbe generating heat and causing the erosion. The free energy of the solidat the homogenized composition is substantially lower than that of theinitial heterogeneous system. Limiting the speed of that reaction couldallow dissipation of the heat and minimize the erosion. This could bedone by slowing down the flow of the infiltrant using some type of flowrestriction.

[0055] Temperature control within the furnace could change the diffusionrate and the solubility of the infiltrant. A temperature variation withtime as the part fills could compensate for heat generation within thepart. Alternatively, a temperature gradient could be set up within thepart. To gain insight into the formation of the erosion paths, visualinspection of the part during the infiltration would show when theerosion develops and how it grows.

[0056] Maintaining the Part's Initial Shape

[0057] Since the processing is done at temperatures close to the meltingpoint of the skeleton, the mechanical strength is very low. Partdistortion was first encountered when suspending odd shaped parts abovethe melt. A mild manifestation of this can be seen in the serpentinepart in FIG. 6. The top leg of the part was initially horizontal, butthe bend widened while it was hanging. This happens during the hightemperature sintering, prior to infiltration. The first step inminimizing the part distortion can be achieved either through changingthe shape of the part or by supporting the part from beneath rather thansuspending it. FIGS. 10 and 11 show how a large part that underwentdistortion while hanging experienced little or no distortion whileresting on the floor of a crucible. For intricate part shapes, this willnot suffice. A loose ceramic powder can be filled around the metal partto support parts with intricate geometry. The infiltration can occureven while the part is embedded in ceramic, since the ceramic powder isnot wet by the infiltrant.

[0058] In this homogenizing infiltration technique, the capillary bodybeing filled is a powder skeleton, rather than a crack or narrow channelas is the case in known techniques for crack filling or brazing. Thispowder skeleton has been created as a net shape or near net shape partthrough a powder metallurgy process such as solid freeform fabricationor metal injection molding. Part size often dictates that the fillingdistance for the infiltrant is much greater than in traditional brazingapplications. The corresponding bulk flow of infiltrant, especiallythrough the entrance region, is quite large and can lead to erosion atthe base of the part. Finally, the isothermal solidification andhomogenization in a powder skeleton is different from in a narrowchannel, with walls of semi-infinite thickness. The final composition ofthe part will be determined by the equilibrium composition of infiltrantand initial powder and their volume fractions.

[0059] Several techniques have been developed to overcome the challengesof a homogenizing infiltration. Gating the infiltration controls thetime the liquid and solid are in contact with each other and preventpremature freezing. Several gating mechanisms are described and somehave been successfully used in practice. Presaturation of the infiltrantis necessary to prevent excessive dissolution of the skeleton.Supporting the part in a bed of loose ceramic powder can preventslumping of delicate parts, since the base material can soften at theinfiltration temperature. A large skeleton should be filled withinfiltrant prior to its isothermal solidification. Choice of materials,powder size and infiltration temperature can maximize the fillingdistance according to the relationships described. A coating can beapplied to the powder to act as a diffusion barrier and slow down thesolidification. The erosion of the skeleton could be caused by anexothermic reaction during the infiltration. Imposing a flow restrictionwould allow time for the generated heat to be dissipated and prevent thedissolution of the skeleton.

[0060] H. Zhuang, J. Chen and E. Lugscheider, “Wide gap brazing ofstainless steel with nickel-base brazing alloys” Welding in the World.Vol. 24, No. 9/10, pp. 200-208 (1986)

[0061] S. Banerjee, R. Oberacker and C. G. Goetzel “Experimental Studyof Capillary Force Induced Infiltration of Compacted Iron Powders withCast Iron”. Modern Developments in Powder Metallurgy. v 16. Metal PowderIndustries Federation: Princeton, N.J. pp. 209-244 (1984)

[0062] K. A. Thorsen, S. Hansen and O. Kjaergaard, “Infiltration ofSintered Steel with a Near-Eutectic Fe—C—P Alloy,” Powder MetallurgyInternational, Vol 15, No. 2, pp. 91-93 (1983)

Having described the invention, what is claimed, is:
 1. A method forfabricating a substantially metal part, comprising the steps of: a.providing a skeleton of nickel alloy powder. material with voidsthroughout; b. providing an infiltrant having a composition thatcomprises: said nickel alloy and a second material, said second materialselected such that said infiltrant has a melting point temperature thatis below the melting point temperature of said nickel alloy alone; c.infiltrating said voids of said skeleton with said infiltrant in liquidform; d. subjecting said infiltrated skeleton to temperature conditionssuch that said second material diffuses from said infiltrated voids intosaid nickel alloy powder material; and e. subjecting said infiltratedskeleton to temperature conditions such that infiltrant that hasinfiltrated into said voids, solidifies.
 2. The method of claim 1, saidstep of subjecting said infiltrated skeleton to temperature conditionssuch that infiltrant solidifies, comprising maintaining said skeleton ata temperature that exceeds said melting temperature of said infiltrant.3. The method of claim 2, said step of maintaining said infiltratedskeleton at a temperature that exceeds said melting point temperature ofsaid infiltrant, comprising maintaining said infiltrated skeleton atsubstantially constant temperature, such that solidification occurssubstantially isothermally.
 4. The method of claim 1 said secondmaterial selected from the group consisting of silicon, phosphorous, tinand boron and combinations thereof.
 5. The method of claim 1, saidsecond material comprising silicon.
 6. The method of claim 1, said stepof providing a skeleton of nickel alloy powder comprising providing askeleton of powder material having a particle size of betweenapproximately 50 μm and approximately 150 μm.
 7. The method of claim 1,said step of providing an infiltrant comprising providing a solution ofsilicon saturated with said nickel alloy.
 8. The method of claim 7, saidstep of providing a solution of silicon saturated with said nickel alloycomprising providing a volume of liquid infiltrant, saturated with saidnickel alloy, and further adding powder of said nickel alloy to saidvolume.
 9. The method of claim 7, said step of infiltrating comprisinginfiltrating said skeleton at a temperature equal to or below a maximumexpected infiltration temperature, and said step of providing aninfiltrant comprising, providing a solution of silicon with said nickelalloy, having a bulk composition that is approximately equal to a bulkcomposition that corresponds with intersection, on an equilibrium phasediagram for said nickel alloy and silicon, of the liquidus line thatincludes zero percent silicon and a line at said maximum expectedinfiltration temperature.
 10. The method of claim 1, said step ofproviding a skeleton comprising providing a skeleton having voids thatform pores having a characteristic radius of less than approximately 80μm.
 11. The method of claim 1, said step of providing a skeletoncomprising providing a skeleton having voids that form pores having acharacteristic length of between approximately 0.08 m and approximately0.5 m.
 12. The method of claim 1, said step of providing a skeletoncomprising providing a skeleton having voids that form pores having acharacteristic length of between approximately 0.08 m and approximately0.5 m and a characteristic radius of less than approximately 80 μm. 13.The method of claim 1, said step of infiltrating said voids of saidskeleton with said infiltrant in liquid form comprising providingconditions such that said infiltrant substantially fully fillssubstantially all of said voids.
 14. The method of claim 13, said stepof providing conditions such that said infiltrant substantially fullyfills substantially all of said voids comprising providing conditionssuch that said infiltrant substantially fully fills substantially all ofsaid voids before said second material has diffused from said infiltrantto a degree sufficient to block additional infiltration.
 15. The methodof claim 1, said step of subjecting said infiltrated skeleton totemperature conditions such that said second material diffusescomprising subjecting said infiltrated skeleton to temperatureconditions such that said second material diffuses from said infiltratedvoids into and substantially throughout said nickel alloy powdermaterial.
 16. The method of claim 1, said step of providing aninfiltrant comprising providing an infiltrant of which said secondmaterial has a diffusivity, relative to said nickel alloy powdermaterial, that is high enough that said second material diffusesthroughout said nickel alloy powder material.
 17. A method forfabricating a substantially metal part, comprising the steps of: a.providing a skeleton of nickel powder material with voids throughout; b.providing an infiltrant having a composition that comprises: nickel anda second material, said second material selected such that saidinfiltrant has a melting point temperature that is below the meltingpoint temperature of nickel alone; c. infiltrating said voids of saidskeleton with said infiltrant in liquid form; d. subjecting saidinfiltrated skeleton to temperature conditions such that said secondmaterial diffuses from said infiltrated voids into said nickel powdermaterial; and e. subjecting said infiltrated skeleton to temperatureconditions such that infiltrant that has infiltrated into said voids,solidifies.
 18. The method of claim 17, said step of subjecting saidinfiltrated skeleton to temperature conditions such that infiltrantsolidifies, comprising maintaining said skeleton at a temperature thatexceeds said melting temperature of said initial composition of saidinfiltrant.
 19. The method of claim 18, said step of maintaining saidinfiltrated skeleton at a temperature that exceeds said melting pointtemperature of said infiltrant, comprising the step of maintaining saidinfiltrated skeleton at substantially constant temperature, such thatsolidification occurs substantially isothermally.
 20. The method ofclaim 17 said second material selected from the group consisting ofsilicon, phosphorous, tin and boron and combinations thereof.
 21. Themethod of claim 17, said infiltrant comprising silicon in an amount lessthan approximately 13% by weight and Nickel in an amount more thanapproximately 87% by weight, said percentages relating to only theNickel and Silicon present, without regard to any other elements presentin said infiltrant.
 22. The method of claim 17, said second materialcomprising silicon, said step of subjecting said infiltrated skeleton totemperature conditions such that infiltrant that has infiltrated intosaid voids, solidifies, comprising the step of maintaining said skeletonat a temperature of between approximately 1150° C. and approximately1400° C.
 23. The method of claim 17, said step of infiltratingcomprising infiltrating said skeleton at a temperature equal to or belowa maximum expected infiltration temperature, and said step of providingan infiltrant comprising, providing a solution of silicon with nickel,having a bulk composition approximately equal to that which correspondswith intersection, on a nickel and silicon equilibrium phase diagram, ofthe liquidus line that includes zero percent silicon and a line at saidmaximum expected infiltration temperature.
 24. The method of claim 17,said step of subjecting said infiltrated skeleton to temperatureconditions such that said second material diffuses, comprisingsubjecting said infiltrated skeleton to temperature conditions such thatsaid second material diffuses from said infiltrated voids into andsubstantially throughout said Nickel powder material.
 25. A method forfabricating a substantially metal part, comprising the steps of: a.providing a skeleton of nickel chromium powder material with voidsthroughout,; b. providing an infiltrant having a composition thatcomprises a nickel chromium silicon alloy, said infiltrant having amelting point temperature that is below the melting point temperature ofnickel chromium alone; c. infiltrating said voids of said skeleton withsaid infiltrant; d. subjecting said infiltrated skeleton to temperatureconditions such that silicon diffuses from said infiltrated voids intosaid nickel chromium powder material; and e. subjecting said infiltratedskeleton to temperature conditions such that infiltrant that hasinfiltrated into said voids, solidifies.
 26. The method of claim 25,said second material selected from the group consisting of silicon,phosphorous, tin and boron and combinations thereof.
 27. The method ofclaim 25, said step of providing a skeleton comprising providing askeleton having voids that form pores having a characteristic radius ofless than approximately 80 μm.
 28. The method of claim 25, said step ofproviding a skeleton comprising providing a skeleton having voids thatform pores having a characteristic length of between approximately 0.08m and approximately 0.5 m.
 29. The method of claim 25, said step ofinfiltrating said voids of said skeleton with said infiltrant in liquidform comprising providing conditions such that said infiltrantsubstantially fully fills substantially all of said voids.
 30. Themethod of claim 29, said step of providing conditions such that saidinfiltrant substantially fully fills substantially all of said voidscomprising providing conditions such that said infiltrant substantiallyfully fills substantially all of said voids before said second materialhas diffused from said infiltrant to a degree sufficient to blockadditional infiltration.
 31. A method for fabricating a substantiallymetal part, comprising the steps of: a. providing a skeleton of hightemperature inconel alloy powder with voids throughout; b. providing aninfiltrant having a composition that comprises an alloy of said hightemperature inconel alloy and a second material selected from the groupconsisting of boron, phosphorous, silicon, tin and a combinationthereof, said infiltrant having a melting point temperature that issignificantly below the melting point temperature of said hightemperature inconel alloy alone; c. infiltrating said voids of saidskeleton with said infiltrant; d. subjecting said infiltrated skeletonto temperature conditions such that said second material diffuses fromsaid infiltrated voids into said inconel powder; and e. subjecting saidinfiltrated skeleton to temperature conditions such that infiltrant thathas infiltrated into said voids, solidifies.
 32. A method forfabricating a substantially metal part, comprising the steps of: a.providing a skeleton of aluminum alloy powder material with voidsthroughout; b. providing an infiltrant having a composition thatcomprises an alloy of said aluminum alloy and a second material selectedfrom the group consisting of silicon and lithium and a combinationthereof, said infiltrant having a melting point temperature that isbelow the melting point temperature of said aluminum alloy of saidpowder, alone; c. infiltrating said voids of said skeleton with saidinfiltrant; d. subjecting said infiltrated skeleton to temperatureconditions such that said second material diffuses from said infiltratedvoids into said aluminum alloy powder; e. subjecting said infiltratedskeleton to temperature conditions such that infiltrant that hasinfiltrated into said voids, solidifies.
 33. The method of claim 32,said step of subjecting said infiltrated skeleton to temperatureconditions such that said second material diffuses comprising subjectingsaid infiltrated skeleton to temperature conditions such that. saidsecond material diffuses from said infiltrated voids into andsubstantially throughout said aluminum alloy powder material.
 34. Themethod of claim 32, said step of infiltrating said voids of saidskeleton with said infiltrant in liquid form comprising providingconditions such that said infiltratant substantially fully fillssubstantially all of said voids.
 35. A method for fabricating asubstantially metal part, comprising the steps of: a. providing askeleton of aluminum powder material with voids throughout; b. providingan infiltrant having a composition that comprises an alloy of aluminumand a second material selected from the group consisting of silicon andlithium and a combination thereof, said infiltrant having a meltingpoint temperature that is below the melting point temperature ofaluminum alone; c. infiltrating said voids of said skeleton with saidinfiltrant; d. subjecting said infiltrated skeleton to temperatureconditions such that said second material diffuses from said infiltratedvoids into said aluminum powder; and e. subjecting said infiltratedskeleton to temperature conditions such that infiltrant that hasinfiltrated into said voids, solidifies.
 36. A method for fabricating asubstantially metal part, comprising the steps of: a. providing askeleton of copper alloy powder material with voids throughout; b.providing an infiltrant having a composition that comprises an alloy ofsaid copper alloy and a second material selected from the groupconsisting of silver and titanium, said infiltrant having a meltingpoint temperature that is below the melting point temperature of saidcopper alloy of said powder, alone; c. infiltrating said voids of saidskeleton with said infiltrant; d. subjecting said infiltrated skeletonto temperature conditions such that said second material diffuses fromsaid infiltrated voids into said copper alloy powder; and e. subjectingsaid infiltrated skeleton to temperature conditions such that infiltrantthat has infiltrated into said voids, solidifies.
 37. The method ofclaim 36, said step of subjecting said infiltrated skeleton totemperature conditions such that said second material diffusescomprising subjecting said infiltrated skeleton to temperatureconditions such that said second material diffuses from said infiltratedvoids into and substantially throughout said copper alloy powdermaterial.
 38. The method of claim 36, said step of infiltrating saidvoids of said skeleton with said infiltrant in liquid form comprisingproviding conditions such that said infiltrant substantially fully fillssubstantially all of said voids.
 39. A method for fabricating asubstantially metal part, comprising the steps of: a. providing askeleton of copper powder with voids throughout; b. providing aninfiltrant having a composition that comprises an alloy of copper and asecond material selected from the group consisting of silver andtitanium, said infiltrant having a melting point temperature that isbelow the melting point temperature of copper alone; c. infiltratingsaid voids of said skeleton with said infiltrant; d. subjecting saidinfiltrated skeleton to temperature conditions such that said secondmaterial diffuses from said infiltrated voids into said copper powder;and e. subjecting said infiltrated skeleton to temperature conditionssuch that infiltrant that has infiltrated into said voids, solidifies.40. A method for fabricating a substantially metal part, comprising thesteps of: a. providing a skeleton of metal powder material with voidsthroughout; b. providing an infiltrant having a composition thatcomprises: said metal powder and a second material, said second materialselected such that said infiltrant has a melting point temperature thatis below the melting point temperature of said metal alone; c.infiltrating said skeleton with said infiltrant by the steps of: i.providing a vessel having a gate mechanism that divides said vessel intoat least two regions, ii. placing said infiltrant in one of saidregions; iii. subjecting said infiltrant to a temperature that isgreater than said melting point temperature of said infiltrant, for atime sufficient to melt said infiltrant; iv. placing said skeleton inanother of said regions; and v. activating said gate to allow saidskeleton and said liquid infiltrant to contact each other at a locationof said skeleton such that infiltrant is drawn into said voids of saidskeleton, at least in part by capillary action; d. subjecting saidinfiltrated skeleton to temperature conditions such that said secondmaterial diffuses from said infiltrated voids into said metal powdermaterial; and e. subjecting said infiltrated skeleton to temperatureconditions such that infiltrant that has infiltrated into said voids,solidifies.
 41. The method of claim 40, further wherein said step ofsubjecting said infiltrated skeleton to temperature conditions such thatsaid second material diffuses from said infiltrated voids into saidmetal powder material comprises subjecting said infiltrated skeleton totemperature conditions such that said second material diffuses from saidinfiltrated voids into and substantially throughout said metal powdermaterial.
 42. The method of claim 40, said gate mechanism comprising amovable divider between said first and second of said regions, said stepof activating said gate comprising moving said gate sufficiently toallow said liquid infiltrant to contact said skeleton.
 43. The method ofclaim 41, said gate mechanism comprising a movable tube having an endthat is shaped to fit against a surface of said crucible, to close saidtube, thereby dividing said vessel into one region within said tube, andanother region outside said tube, said step of activating said gatecomprising moving said tube away from said vessel wall sufficiently toallow said liquid infiltrant to flow out of said tube and to contactsaid skeleton.
 44. The method of claim 40, said step of infiltratingsaid voids of said skeleton with said infiltrant in liquid formcomprising providing conditions such that said infiltrant substantiallyfully fills substantially all of said voids.
 45. A method forfabricating a substantially metal part, comprising the steps of: a.providing a skeleton of metal powder material with voids throughout; b.providing an infiltrant having a composition that comprises: said metalpowder and a second material, said second material selected such thatsaid infiltrant has a melting point temperature that is significantlybelow the melting point temperature of said metal alone; c. infiltratingsaid skeleton with said infiltrant by the steps of: i. providing aquantity of said infiltrant in liquid form; ii. interposing a stiltbetween said skeleton and said liquid infiltrant, ii. contacting saidstilt to said liquid infiltrant such that infiltrant is drawn into saidvoids of said skeleton, at least in part by capillary action, passingfirst through said stilt and then into said skeleton; d. subjecting saidinfiltrated skeleton to temperature conditions such that said secondmaterial diffuses from said infiltrated voids into said metal powdermaterial; and e. subjecting said infiltrated skeleton to temperatureconditions such that infiltrant that has infiltrated into said voids,solidifies.
 46. The method of claim 45, said step of subjecting saidinfiltrated skeleton to temperature conditions such that said secondmaterial diffuses comprising subjecting said infiltrated skeleton totemperature conditions such that said second material diffuses from saidinfiltrated voids into and substantially throughout said metal powdermaterial.
 47. The method of claim 45, said step of infiltrating saidvoids of said skeleton with said infiltrant in liquid form comprisingproviding conditions such that said infiltrant substantially fully fillssubstantially all of said voids.
 48. A method for fabricating asubstantially metal part, comprising the steps of: a. providing askeleton of metal powder material with voids throughout; b. providing aninfiltrant having a composition that comprises: said metal powder and asecond material, said second material selected such that said infiltranthas a melting point temperature that is below the melting pointtemperature of said metal alone; c. infiltrating said skeleton with saidinfiltrant by the steps of: i. providing a quantity of infiltrant; ii.subjecting said infiltrant to a temperature that is greater than saidmelting point temperature of said infiltrant, for a time sufficient tomelt said quantity of infiltrant; iii. suspending said skeleton abovesaid quantity of said liquid infiltrant; and iv. bringing said skeletonand said infiltrant into contact so that said skeleton contacts saidliquid infiltrant at a location of said skeleton such that infiltrant isdrawn into said voids of said skeleton, at least in part by capillaryaction; d. subjecting said skeleton to temperature conditions such thatsaid second element diffuses from said infiltrated voids into said metalpowder material; and e. subjecting said infiltrated skeleton totemperature conditions such that infiltrant that has infiltrated intosaid voids, solidifies.
 49. The method of claim 48, said step ofsubjecting said infiltrated skeleton to temperature conditions such thatsaid second material diffuses comprising subjecting said infiltratedskeleton to temperature conditions such that said second materialdiffuses from said infiltrated voids into and substantially throughoutsaid metal powder material.
 50. The method of claim 49, said step ofinfiltrating said voids of said skeleton with said infiltrant in liquidform comprising providing conditions such that said infiltrantsubstantially fully fills substantially all of said voids.
 51. A methodfor fabricating a substantially metal part, comprising the steps of: a.providing a skeleton of metal powder material with voids throughout; b.filling a ceramic powder around said skeleton to a degree that willsupport said skeleton against slumping during subsequent steps atelevated temperature; c. providing an infiltrant having a compositionthat comprises: said metal powder and a second material, said secondmaterial selected such that said infiltrant has a melting pointtemperature that is below the melting point temperature of said metalalone; d. infiltrating said skeleton with said infiltrant by the stepsof: i. providing a quantity of infiltrant; ii. arranging said infiltrantand said skeleton spaced apart from each other; iii. subjecting saidinfiltrant to a temperature that is greater than said melting pointtemperature of said infiltrant, for a time sufficient to melt saidquantity of infiltrant; and iv. contacting said skeleton to said meltedinfiltrant at a location of said skeleton such that infiltrant is drawninto said voids of said skeleton, at least in part by capillary action;e. subjecting said infiltrated skeleton to temperature conditions suchthat said second element diffuses from said infiltrated voids into saidmetal powder material; and f. subjecting said infiltrated skeleton totemperature conditions such that infiltrant that has infiltrated intosaid void, solidifies.
 52. The method of claim 51, said step ofsubjecting said infiltrated skeleton to temperature conditions such thatsaid second material diffuses comprising subjecting said infiltratedskeleton to temperature conditions such that said second materialdiffuses from said infiltrated voids into and substantially throughoutsaid metal powder material.
 53. The method of claim 51, said step ofinfiltrating said voids of said skeleton with said infiltrant in liquidform comprising providing conditions such that said infiltrantsubstantially fully fills substantially all of said voids.
 54. A methodfor fabricating a substantially metal part, comprising the steps of: a.providing a skeleton of metal powder with voids throughout, said voidsforming pores having a characteristic length of between approximately0.08 m and approximately 0.5 m; b. providing an infiltrant having acomposition that comprises: said metal and a second material, saidsecond material selected such that said infiltrant has a melting pointtemperature that is below the melting point temperature of said metalalone; c. infiltrating substantially all of said voids of said skeletonsubstantially fully, with said infiltrant in liquid form; d. subjectingsaid infiltrated skeleton to temperature. conditions such that saidsecond material diffuses from said infiltrated voids into said metalpowder material; and e. subjecting said infiltrated skeleton totemperature conditions such that infiltrant that has infiltrated intosaid voids, solidifies.
 55. The method of claim 54, said step ofsubjecting said infiltrated skeleton to temperature conditions such thatsaid second material diffuses comprising subjecting said infiltratedskeleton to temperature conditions such that said second materialdiffuses from said infiltrated voids into and substantially throughoutsaid metal powder material.
 56. The method of claim 54, furthercomprising the step of selecting: a. powder material having a granulerepresentative size; b. infiltrant having a viscosity; c. infiltranthaving a diffusivity in said powder material; and d. a finished partgeometry having a maximum height; such that said infiltrant infiltratesto a sufficient rate, to said maximum geometry height, before saidsecond element has diffused out from said infiltrant that hasinfiltrated said voids to a degree that would result in said infiltrantsolidifying and blocking off further infiltration.
 57. The method ofclaim 56, said step of selecting comprising the step of adjusting atleast one of the following factors as indicated: a. decreasing saidrepresentative size of said powder material to achieve relativelygreater maximum capillary driving rise height in said geometry; b.increasing said representative size of said powder material to achieve arelatively faster rate of infiltration; and c. increasing saidrepresentative pore size of said skeleton to achieve a relatively longerperiod of time before solidification that blocks off furtherinfiltration.